Pneumatic tire

ABSTRACT

A tread pattern of a pneumatic tire includes two or more circumferential main grooves in a half region demarcated by the equatorial plane, and land portions defined by the circumferential main grooves. A center land portion closest among the land portions to the equatorial plane includes a center sipe extending in the width direction, the center sipe is a composite sipe including a two-dimensional portion and three-dimensional portions provided on both sides of the two-dimensional portion in the width direction, a middle land portion that is adjacent to an outer side of the center land portion in the width direction includes a middle sipe extending in the width direction, and the middle sipe is a composite sipe comprising a two-dimensional portion provided on an inner side in the width direction and a three-dimensional portion provided on an outer side of the two-dimensional portion in the width direction.

TECHNICAL FIELD

The present technology relates to a pneumatic tire.

BACKGROUND ART

Japan Unexamined Patent Publication No. 2017-43208 describes a pneumatictire that is designed to provide drainage performance and uneven wearresistance performance in a compatible manner. In Japan UnexaminedPatent Publication No. 2017-43208, a recess portion is provided in thegroove wall of the main groove, and a sipe communicating with the recessportion and a shallow groove communicating with the other portion thanthe recess portion are provided. Japan Patent No. 5948995 also describesa pneumatic tire that can provide on-snow performance and uneven wearresistance performance in a compatible manner. In Japan Patent No.5948995, the sipe density on a vehicle inner side is increased and alarge number of three-dimensional sipes are disposed on the vehicleinner side, designed to provide snow performance and uneven wearresistance performance in a compatible manner.

In the pneumatic tires of Japan Unexamined Patent Publication No.2017-43208 described above, the improvement of braking performance onsnow-covered road surfaces, in other words, braking on snow performance,as well as steering stability performance on snow-covered road surfaces,in other words, handling on snow performance has not been considered,and there is room for improvement. Also, in the pneumatic tires of JapanPatent No. 5948995 described above, there is room for improvement ofpattern noise performance.

SUMMARY

The present technology provides a pneumatic tire having improved theuneven wear resistance performance, braking on snow performance,handling on snow performance, and pattern noise performance in awell-balanced manner.

A pneumatic tire according to an aspect of the present technology is apneumatic tire including a tread pattern, the tread pattern includingtwo or more circumferential main grooves provided in a half regiondemarcated by a tire equatorial plane, and a plurality of land portionsdefined by the circumferential main grooves, a center land portion thatis the closest land portion of the plurality of land portions to thetire equatorial plane including a center sipe extending in a tire widthdirection, the center sipe being a composite sipe including atwo-dimensional portion and three-dimensional portions provided on bothsides of the two-dimensional portion in the tire width direction, amiddle land portion that is a land portion adjacent to an outer side ofthe center land portion in the tire width direction including a middlesipe extending in the tire width direction, and the middle sipe being acomposite sipe including a two-dimensional portion provided on an innerside in the tire width direction and a three-dimensional portionprovided on an outer side of the two-dimensional portion in the tirewidth direction.

A ratio of a total length of the three-dimensional portions of thecenter sipe in the tire width direction to a length of the center sipein the tire width direction is preferably 0.30 or more and 0.70 or less.

The center sipe preferably has a Z-shape with two bent portions.

A ratio of a length of the three-dimensional portion of the middle sipein the tire width direction to a length of the middle land portion inthe tire width direction is preferably 0.25 or more and 0.80 or less.

The middle sipe has a Z-shape with two bent portions, and a ratio of adistance in the tire width direction between a bent portion that is acloser of the two bent portions to a center line, the center linepassing through a midpoint position of the land portion in the tirewidth direction, and the center line to a width of the land portion inthe tire width direction is preferably 0 or more and 0.40 or less.

An edge on an outer side of the middle land portion in the tire widthdirection is a zigzag edge having a zigzag shape withrecesses/protrusions that has a position periodically changing in thetire width direction, an edge on an inner side of the middle landportion in the tire width direction has a straight shape, and thethree-dimensional portion of the middle sipe is preferably connected tothe zigzag edge.

The middle sipe is preferably connected to a maximum amplitude positionof the zigzag edge in the tire width direction.

A ratio of a minimum value of distances between protrusion portions ofthe zigzag shape to a maximum value of the distances between theprotrusion portions of the zigzag shape is preferably 0.50 or more.

The middle land portion preferably includes a plurality of lug groovesand, between the lug grooves that are adjacent, two or more of themiddle sipes and three or more protrusion portions of the zigzag shape.

Distances in the tire circumferential direction between connectionportions of the two or more middle sipes with the circumferential maingroove on the inner side in the tire width direction, the two or moremiddle sipes provided between the lug grooves that are adjacent, areLs1, Ls2, . . . , Lsn, where n is a natural number of three or greater,and preferably, Ls1<Lsn.

Distances in the tire circumferential direction between connectionportions of the two or more middle sipes with a circumferential maingroove on the inner side in the tire width direction, the two or moremiddle sipes provided between the lug grooves that are adjacent, areLs1, Ls2, . . . , Lsn, where n is a natural number of three or greater,distances in the tire circumferential direction between the protrusionportions of connection portions of a plurality of the middle sipes withthe circumferential main groove on an outer side in the tire widthdirection, the plurality of middle sipes provided between the luggrooves that are adjacent, are Lz1, Lz2, . . . , Lzn, where n is anatural number of three or greater, and preferably, Ls1<Lz1 and Lsn>Lzn.

The pneumatic tire further including a shoulder land portion that is aland portion on an outer side of the middle land portion in the tirewidth direction, wherein the shoulder land portion includes a shouldersipe extending in the tire width direction, the shoulder sipe ispreferably a composite sipe including a three-dimensional portionprovided on the inner side in the tire width direction and atwo-dimensional portion provided on an outer side of thethree-dimensional portion in the tire width direction.

A ratio of a length of the three-dimensional portion of the shouldersipe in the tire width direction to a ground contact width of theshoulder land portion in the tire width direction is preferably 0.25 ormore and 0.65 or less.

Groove wall surfaces of both sides of the circumferential main groovebetween the middle land portion and the shoulder land portion arepreferably wall surfaces in which zigzag edges face each other.

According to embodiments of the present technology, an effect ofimproving the uneven wear resistance performance, braking on snowperformance, handling on snow performance, and pattern noise performancein a well-balanced manner is achieved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view in a tire meridian directionillustrating a pneumatic tire according to an embodiment of the presenttechnology.

FIG. 2 is a developed view illustrating an example of a tread pattern ofthe pneumatic tire illustrated in FIG. 1.

FIG. 3 is an enlarged view of a part of a center land portion of thetread pattern illustrated in FIG. 2.

FIG. 4 is an enlarged view of a part of a middle land portion of thetread pattern illustrated in FIG. 2.

FIG. 5 is a plan view illustrating an example of a sipe.

FIG. 6 is an enlarged view of a part of a middle land portion of thetread pattern illustrated in FIG. 2.

FIG. 7 is an enlarged view of a part of a middle land portion of thetread pattern illustrated in FIG. 2.

FIG. 8A is an enlarged view of a part of a middle land portion of thetread pattern illustrated in FIG. 2.

FIG. 8B is an enlarged view illustrating a part of FIG. 8A.

FIG. 9A is a diagram illustrating another example of the middle landportion.

FIG. 9B is an enlarged view illustrating a part of FIG. 9A.

FIG. 10A is a diagram illustrating another example of the middle landportion.

FIG. 10B is an enlarged view illustrating a part of FIG. 10A.

FIG. 11 is a cross-sectional view of a lug groove along an extensiondirection in FIG. 2.

FIG. 12 is an enlarged view of a part of a shoulder land portion of thetread pattern illustrated in FIG. 2.

FIG. 13 is a view illustrating the inclination direction of each sipe inFIG. 2.

FIG. 14 is a cross-sectional view illustrating an example of athree-dimensional portion of a composite sipe in FIG. 2.

FIG. 15 is a cross-sectional view of the sipe of FIG. 5 along anextension direction.

DETAILED DESCRIPTION

Embodiments of the present technology are described in detail below withreference to the drawings. In the embodiments described below, identicalor substantially similar components to those of other embodiments haveidentical reference signs, and descriptions of those components areeither simplified or omitted. The present technology is not limited bythe embodiments. Constituents of the embodiments include elements thatare substantially identical or that can be substituted and easilyconceived by one skilled in the art. The plurality of modified examplesdescribed in the embodiments can be combined as desired within the scopeapparent to one skilled in the art. Moreover, various omissions,substitutions, and changes to the configurations can be carried outwithin the scope of the present technology.

Pneumatic Tire

FIG. 1 is a cross-sectional view in a tire meridian directionillustrating a pneumatic tire according to an embodiment of the presenttechnology. FIG. 1 is a cross-sectional view of a half region in a tireradial direction. Additionally, FIG. 1 illustrates a radial tire for apassenger vehicle as an example of a pneumatic tire.

“Cross-section in the tire meridian direction” refers to a cross sectionof the tire taken along a plane that includes the tire rotation axis(not illustrated). A reference sign CL denotes a tire equatorial planeand refers to a plane perpendicular to the tire rotation axis thatpasses through the center point of the tire in a tire rotation axisdirection. “Tire radial direction” refers to the direction orthogonal tothe rotation axis (not illustrated) of a pneumatic tire 10, “inner sidein the tire radial direction” refers to the side toward the rotationaxis in the tire radial direction, “outer side in the tire radialdirection” refers to the side away from the rotation axis in the tireradial direction. In addition, “tire circumferential direction” refersto the circumferential direction with the rotation axis as the centeraxis. In addition, “tire width direction” refers to a direction parallelwith the tire rotation axis. “Inner side in the tire width direction”refers to the side toward the tire equatorial plane CL in the tire widthdirection, and “outer side in the tire width direction” refers to theside away from the tire equatorial plane CL in the tire width direction.

“Tire equatorial plane CL” refers to a plane orthogonal to the rotationaxis of the pneumatic tire 10 that passes through the center of the tirewidth of the pneumatic tire 10. “Tire width” is the width in the tirewidth direction between components located on outer sides in the tirewidth direction, or in other words, the distance between the componentsthat are the most distant from the tire equatorial plane CL in the tirewidth direction. “Tire equator line” refers to a line along the tirecircumferential direction of the pneumatic tire 10 that lies on the tireequatorial plane CL. In the present embodiment, the tire equator lineand the tire equatorial plane are denoted by the same reference sign CL.

As illustrated in FIG. 1, the pneumatic tire 10 according to the presentembodiment includes an annular tread portion 1 extending in the tirecircumferential direction, a pair of sidewall portions 2, 2 disposed onboth sides of the tread portion 1, and a pair of bead portions 3, 3disposed on the inner side in the tire radial direction of the pair ofsidewall portions 2.

A carcass layer 4 is mounted between the pair of bead portions 3, 3. Thecarcass layer 4 includes a plurality of reinforcing cords extending inthe tire radial direction and is folded back around a bead core 5disposed in each of the bead portions 3 from a tire inner side to a tireouter side. A bead filler 6 having a triangular cross-sectional shapeand formed of a rubber composition is disposed on the outercircumference of the bead core 5.

On the other hand, a plurality of belt layers 7 are embedded on theouter circumferential side of the carcass layer 4 in the tread portion1. Each of the belt layers 7 includes a plurality of reinforcing cordsthat are inclined with respect to the tire circumferential direction,and the reinforcing cords are disposed so as to intersect each otherbetween the layers. In the belt layers 7, the inclination angle of thereinforcing cords with respect to the tire circumferential direction isset to fall within a range of from 10° to 40°, for example. Steel cordsare preferably used as the reinforcing cords of the belt layers 7. Toimprove high-speed durability, at least one belt cover layer 8, formedby disposing reinforcing cords at an angle of, for example, not greaterthan 5° with respect to the tire circumferential direction, is disposedon an outer circumferential side of the belt layers 7. Organic fibercords such as nylon and aramid are preferably used as the reinforcingcords of the belt cover layer 8.

Note that the tire internal structure described above represents atypical example for a pneumatic tire, and the pneumatic tire is notlimited thereto.

Tread Portion

FIG. 2 is a developed view illustrating an example of a tread pattern ofthe pneumatic tire 10 illustrated in FIG. 1. The reference sign Tdenotes a tire ground contact edge in FIGS. 1 and 2.

As illustrated in FIG. 2, the pneumatic tire 10 of the present exampleincludes four circumferential main grooves 11A, 11B, 12A, and 12B in thetread portion 1. The circumferential main grooves 12A and 12B extend inthe tire circumferential direction at positions on an outer side of thetire equatorial plane CL in the tire width direction. Thecircumferential main groove 11A extends in the tire circumferentialdirection at a position closer to the tire equatorial plane CL than thecircumferential main groove 12A. The circumferential main groove 11Bextends in the tire circumferential direction at a position closer tothe tire equatorial plane CL than the circumferential main groove 12B.

The circumferential main grooves 11A, 11B, 12A, and 12B arecircumferential grooves with a wear indicator that indicates theterminal stage of wear and typically have a groove width of 5.0 mm ormore and a groove depth of 7.5 mm or more. Note that the groove widthsand groove depths of the circumferential main grooves 11A, 11B, 12A, and12B are not limited to the ranges described above.

Moreover, “lug groove” refers to a lateral groove having a groove widthof 2.0 mm or more and a groove depth of 3.0 mm or more. Additionally,“sipe”, which is described below, refers to a cut formed in a landportion that typically has a groove width of less than 1.5 mm.

In FIG. 2, a center land portion Rc is defined by the twocircumferential main grooves 11A and 11B. In addition, one middle landportion Rm is defined by the two circumferential main grooves 11A and12A, and the other middle land portion Rm is defined by the twocircumferential main grooves 11B and 12B. One shoulder land portion Rsis on an outer side of the circumferential main groove 12A in the tirewidth direction. The other shoulder land portion Rs is on an outer sideof the circumferential main groove 12B in the tire width direction. Notethat when three circumferential main grooves are provided, no centerland portion Rc is provided, and the tread portion includes: the middleland portions Rm on both sides of the equator line CL; and the shoulderland portions Rs each on an outer side of the middle land portions Rm inthe tire width direction.

The center land portion Rc (hereinafter, also referred to simply as theland portion Rc) is located on the tire equator line CL. The landportion Rc includes a plurality of sipes 15. The sipes 15 extend in thetire circumferential direction and the tire width direction. One end ofthe sipe 15 is connected to the circumferential main groove 11A, and theother end of the sipe 15 is connected to the circumferential main groove11B. The sipe 15 is a through sipe extending through the land portionRc. Note that in the present example, the edges on both sides of theland portion Rc have straight shapes.

The middle land portion Rm (hereinafter, also simply referred to as theland portion Rm) has a plurality of lug grooves 13. The lug grooves 13extend in the tire width direction and the tire circumferentialdirection. One end on an inner side of the lug groove 13 in the tirewidth direction opens to the circumferential main groove 11A or 11B. Theother end on an outer side of the lug groove 13 in the tire widthdirection opens to the circumferential main groove 12A or 12B. The landportion Rm has a raised bottom portion 130 in the lug groove 13. Theraised bottom portion 130 is a portion where the groove bottom of thelug groove 13 is raised so that the groove depth is shallower than otherportions. The raised bottom portion 130 is provided on an end portion onthe inner side of the lug groove 13 in the tire width direction. Theland portion Rm also includes a plurality of sipes 16 between theadjacent lug grooves 13. The sipes (hereinafter, also referred to as“middle sipe”) 16 extend in the tire circumferential direction and thetire width direction. One end of the sipe 16 is connected to thecircumferential main groove 11A or 11B, and the other end of the sipe 16is connected to the circumferential main groove 12A or 12B. The sipe 16is a through sipe extending through the land portion Rm.

In the present example, an edge on an outer side of the land portion Rmin the tire width direction, in other words, an edge on thecircumferential main groove 12A or 12B side, has a zigzag shape(hereinafter may be referred to as a zigzag edge). The zigzag shape is ashape with recesses/protrusions that has a position periodicallychanging in the tire width direction. An edge on an inner side of theland portion Rm in the tire width direction, in other words, an edge onthe circumferential main groove 11A or 11B side, has a straight shapethat does not have recess/protrusion.

The shoulder land portion Rs (hereinafter, also simply referred to asthe land portion Rs) has a plurality of lug grooves 14A, 14B. The luggrooves 14A, 14B extend in the tire width direction from the inner sidein the tire width direction toward the outer side in the tire widthdirection. The lug grooves 14A, 14B extend from the circumferential maingrooves 12A or 12B to positions on an outer side of the tire groundcontact edge T. The land portion Rs has a plurality of sipes 17 betweenthe lug groove 14A and the lug groove 14B. The sipes 17 extend in thetire width direction. One end of the sipe 17 is connected to thecircumferential main groove 12A or 12B, and the other end of the sipe 17is connected to a decorative groove 18 on the outer side of the tireground contact edge T.

In the present example, the land portion Rs has raised bottom portions140A, 140B in the lug grooves 14A, 14B. The raised bottom portions 140A,140B are portions where the groove bottom of the lug grooves 14A, 14Bare raised so that the groove depth is shallower than other portions.The raised bottom portions 140A, 140B are provided at the end portionson an inner side of the lug grooves 14A, 14B in the tire widthdirection, in other words, at open ends of the circumferential maingrooves 12A, 12B.

Sipe

In FIG. 2, the sipes 15, 16, and 17 are composite sipes each having asection of two-dimensional portion (so-called planar sipe) and a sectionof three-dimensional portion (so-called 3D sipe). “Two-dimensionalportion” refers to a portion having a sipe wall surface having a linearshape when viewed in a cross-sectional view perpendicular to the lengthdirection of the sipe. “Three-dimensional portion” refers to a portionhaving a sipe wall surface having a shape bent in a sipe width directionwhen viewed in a cross-sectional view perpendicular to the lengthdirection of the sipe. The sipes 15, 16, and 17 ensure the edgecomponents of the land portions Rc, Rm, and Rs, and the tractioncharacteristics of the pneumatic tire 10 is improved.

In FIG. 2, a section of the sipe 15 in a region 20A is athree-dimensional portion. A section of the sipe 15 other than theregion 20A is a two-dimensional portion. A section of the sipe 16 in aregion 20B is a three-dimensional portion. A section of the sipe 16other than the region 20B is a two-dimensional portion. A section of thesipe 17 in a region 20C is a three-dimensional portion. A section of thesipe 17 other than the region 20C is a two-dimensional portion.

The two-dimensional portion has a sipe wall surface having a straightshape in any cross-sectional view (cross-sectional view including thesipe width direction and a sipe depth direction), where a sipe lengthdirection is the normal direction. The three-dimensional portion has asipe wall surface having a bent shape with an amplitude in the sipewidth direction in both a cross-sectional view in which the sipe lengthdirection is a normal direction and a cross-sectional view in which thesipe depth direction is a normal direction. The three-dimensionalportion has an effect of reinforcing the rigidity of the land portionbecause the meshing force of the opposing sipe wall surfaces is strongerthan the two-dimensional portions. By increasing the rigidity of thezigzag shaped portion of the land portion, the tire chip resistanceperformance can be improved.

Here, focusing on the land portion Rm defined by the circumferentialmain groove 11A and the circumferential main groove 12A, the edge on thecircumferential main groove 12A side has a zigzag shape. In other words,one of the edges of the land portion Rm in the tire width direction hasa zigzag shape. In addition, the region 20B is on the edge side that hasa zigzag shape. In other words, the three-dimensional portion of thesipe 16 is connected to an edge that has a zigzag shape, in other words,a zigzag edge. As a result, the land portion Rm improves snowperformance due to the edge effect of the zigzag shape. Furthermore,because the sipe 16 in the portion connected to the circumferential maingroove 12A on the edge side having a zigzag shape is a three-dimensionalportion, the block rigidity of the portion of the zigzag shapeincreases, and the tire chip resistance performance is improved.

In addition, focusing on the land portion Rs, an edge on thecircumferential main groove 12A side has a zigzag shape. In other words,one of the edges of the land portion Rs in the tire width direction hasa zigzag shape. In addition, the region 20C is on the edge side that hasa zigzag shape. In other words, the three-dimensional portion of thesipe 17 is connected to an edge that has a zigzag shape, in other words,a zigzag edge. As a result, the land portion Rs improves snowperformance due to the edge effect of the zigzag shape. Furthermore,because the sipe 17 in the portion connected to the circumferential maingroove 12A on the edge side having a zigzag shape is a three-dimensionalportion, the block rigidity of the portion of the zigzag shapeincreases, and the tire chip resistance performance is improved.

Focusing on the circumferential main groove 12A between the land portionRm and the land portion Rs, the groove wall surfaces on both sides ofthe circumferential main groove 12A are wall surfaces in which thezigzag edges face each other. This increases the edge effect andimproves snow performance.

Also, focusing on the land portion Rs, a three-dimensional portion isdisposed at one end of the sipe 17 that connects to the circumferentialmain groove 12A or 12B between the land portion Rs and the land portionRm, and a two-dimensional portion is disposed on the other end of thesipe 17. By disposing in this manner, degradation of pattern noise dueto an increase in block rigidity can be suppressed while improving theuneven wear resistance performance of the land portion Rm.

FIG. 3 is an enlarged view of a part of the center land portion Rc ofthe tread pattern illustrated in FIG. 2. In FIG. 3, the sipe 15 of theland portion Rc (hereinafter, also referred to as a center sipe) has asection of a two-dimensional portion that transverses the tireequatorial plane CL and a section of the region 20A of three-dimensionalportion provided on both sides of the section of the two-dimensionalportion in the tire width direction. Note that in FIG. 3, the landportion Rc does not include lug grooves.

Here, a maximum width of the land portion Rc in the tire width directionis denoted as Wc, and a length of the region 20A of three-dimensionalportion in the tire width direction is denoted as Wc3. In this case, aratio Wc3/Wc is preferably 0.30 or more and 0.70 or less. When the ratioWc3/Wc is less than 0.30, sufficient block rigidity will not beobtained, and wear resistance performance decreases, which is notpreferable. When the ratio Wc3/Wc is greater than 0.70, block rigidityon the three-dimensional portion side will be too high, and patternnoise will be negatively affected, which is not preferable.

The center sipe 15 has a generally Z-shape with two bent portions. Agenerally Z-shape of the center sipe 15 is provided in thetwo-dimensional portion. Because the center sipe 15 has a generallyZ-shape, the edge effect is increased, and the snow performance isimproved.

The center sipe 15 is a composite sipe having a two-dimensional portionand three-dimensional portions provided on both sides of thetwo-dimensional portion. Thus, the three-dimensional portion of thecenter sipe 15 and the two-dimensional portion of the middle landportion Rm are disposed so as to face each other. As a result, excessivereduction in block rigidity at or near the circumferential main grooves11A, 11B on the tire equatorial plane CL side is suppressed, and theuneven wear resistance performance at or near the tire equatorial planeCL can be improved.

Middle Land Portion

FIG. 4 is an enlarged view of a part of the middle land portion Rm ofthe tread pattern illustrated in FIG. 2. In FIG. 4, a maximum width ofthe land portion Rm in the tire width direction is denoted as W1. Also,in FIG. 4, a distance (length) in the tire width direction from aconnection portion of the sipe 16 with the circumferential main groove11A to an edge on an inner side of the region 20B in the tire widthdirection, which is a section of the three-dimensional portion, isdenoted as Wc1. The distance Wc1 is the length of the two-dimensionalportion of the sipe 16 in the tire width direction. In FIG. 4, adistance from a connection portion of the sipe 16 with thecircumferential main groove 12A to an edge on the inner side of theregion 20B in the tire width direction, which is a section of thethree-dimensional portion, is denoted as Wc2. Here, a length that is asum of the length Wc1 and the length Wc2 is denoted as Wm. The length Wmis a length of the entire sipe 16 in the tire width direction. In thiscase, a ratio Wc2/Wm is preferably 0.25 or more and 0.80 or less. Whenthe ratio Wc2/Wm is less than 0.25, sufficient block rigidity will notbe obtained, and steering stability performance will be negativelyaffected, which is not preferable. When the ratio Wc2/Wm is greater than0.80, block rigidity will be too high, and pattern noise will benegatively affected, which is not preferable.

Also, a ratio Wc1/Wm is preferably 0.20 or more and 0.70 or less. Whenthe ratio Wc1/Wm is less than 0.20, the block rigidity of the sipe 16 onthe circumferential main groove 11A side will be too high, which is notpreferable. When the ratio Wc1/Wm is greater than 0.70, the blockrigidity of the sipe 16 on the circumferential main groove 11A side willbe too low, which is not preferable.

Z-Shape

FIG. 5 is a plan view illustrating an example of the sipe 16. In FIG. 5,one end of the sipe 16 is connected to the circumferential main groove11A, and the other end is connected to the circumferential main groove12A. With reference to FIG. 5, the sipe 16 of the present exampleincludes linear portions ST1, ST2, and ST3, and bent portions C1 and C2.The linear portion ST1 is disposed on the circumferential main groove11A side, in other words, on the inner side in the tire width direction.The linear portion ST1 is connected to the edge on the inner side of theland portion Rm in the tire width direction. The linear portion ST3 isdisposed on the circumferential main groove 12A side, in other words, onthe outer side in the tire width direction. The linear portion ST3 isconnected to the edge on the outer side of the land portion Rm in thetire width direction. A length of the linear portion ST1 in theextension direction is shorter than a length of the linear portion ST3in the extension direction.

One end of the linear portion ST1 is connected to the circumferentialmain groove 11A, and the other end of the linear portion ST1 isconnected to one end of the bent portion C1. The other end of the bentportion C1 is connected to the linear portion ST2. One end of the linearportion ST3 is connected to the circumferential main groove 12A, and theother end of the linear portion ST3 is connected to one end of the bentportion C2. The other end of the bent portion C2 is connected to thelinear portion ST2. In this way, the bent portion C1 is provided betweenthe linear portion ST1 and the linear portion ST2 and the bent portionC2 is provided between the linear portion ST2 and the linear portionST3, and thus the sipe 16 has a generally Z-shape. The Z-shape is ashape including at least two bent portions and having the linearportions connected to each other by the bent portions. Note that theZ-shape may include an S-shape formed of an arc. Hereinafter, of thelinear portion ST1 and the linear portion ST3, the linear portion ST1that is closer to the equatorial plane CL may be referred to as an innerside linear portion, and the linear portion ST3 that is further from theequatorial plane CL may be referred to as an outer side linear portion.

FIG. 6 is an enlarged view of a part of the middle land portion Rm ofthe tread pattern illustrated in FIG. 2. In FIG. 6, in a block definedby the adjacent lug grooves 13 of the plurality of lug grooves 13extending through the land portion Rm, a length of the edge of thezigzag shape between the adjacent lug grooves 13 in the tirecircumferential direction is denoted as L1. A distance betweenprotrusion portions of the zigzag shape in the tire circumferentialdirection is denoted as L2. A ratio L2/L1 of the distance L2 to thelength L1 is preferably 0.15 or more and 0.55 or less. When the ratioL2/L1 is greater than 0.55, the edge effect cannot be sufficientlyachieved, and the snow performance does not improve, which is notpreferable. When the ratio L2/L1 is less than 0.15, recesses/protrusionsof the zigzag shape are excessively fine and chip easily, which is notpreferable. Note that the length L1 of the edge of the zigzag shape inthe tire circumferential direction is measured with reference to thecorner portions that are the intersection points of the lug grooves 13and the circumferential main groove 12A.

Also, in FIG. 6, a maximum width of the land portion Rm in the tirewidth direction is denoted as W1. A length (in other words, a width) inthe tire width direction from a connection point of the sipe 16 with thecircumferential main groove 11A on the inner side in the tire widthdirection to an end point K1 on the outer side of the inner side linearportion ST1 in the tire width direction is denoted as W2. In a blockdefined by the adjacent lug grooves 13 of the plurality of lug grooves13 extending through the land portion Rm, a width that is two-times anamplitude of the zigzag shape in the tire width direction is denoted asW3. The width W3 is a distance in the tire width direction between acorner portion 21 and a corner portion 22 at an opening of the sipe 16.

In this case, a ratio W2/W1 of the width W2 to the width W1 ispreferably 0.10 or more and 0.40 or less. When the ratio W2/W1 is lessthan 0.10, the edge effect is reduced, and the snow performance isdegraded, which is not preferable. When the ratio W2/W1 is greater than0.40, the bent portion C1 is close to the zigzag portion, and the tirechip resistance performance is poor, which is not preferable.

A ratio W3/W2 of the width W3 to the width W2 is preferably 0.15 or moreand 0.45 or less. When the ratio W3/W2 is less than 0.15, the edgeeffect of the zigzag groove is reduced, and the snow performance isdegraded, which is not preferable. When the ratio W3/W2 is greater than0.45, drainage properties are degraded, and the edge effect of the sipes16 is also reduced, and thus the snow performance is degraded, which isnot preferable.

Additionally, a ratio W3/W1 of the width W3 to the maximum width W1 ofthe land portion Rm in the tire width direction is preferably 0.03 ormore and 0.15 or less. When the ratio W3/W1 is greater than 0.15,drainage properties are impaired, and drainage performance is degraded,which is not preferable. When the ratio W3/W1 is less than 0.03, theedge effect is not achieved and the snow performance does not improve,which is not preferable.

Incidentally, in the land portion Rm, preferably, two or more of thesipes 16 are provided between the adjacent lug grooves 13, and three ormore protrusion portions of the zigzag shape are provided between theadjacent lug grooves 13. When there are less than two sipes 16 betweenthe adjacent lug grooves 13, the number of the protrusion portions ofthe zigzag shape is reduced and snow performance does not improve, whichis not preferable.

Additionally, in FIG. 6, the respective linear portions ST3 of theplurality of sipes 16 are parallel to each other. Here, “parallel” meansthat an angle formed by two straight lines L16 that extend therespective center lines of the two sipes 16 is within ±5°. When the twostraight lines L16 are completely parallel, the angle formed by the twostraight lines L16 is 0°.

Furthermore, in FIG. 6, the plurality of lug grooves 13 are parallel toeach other. Here, “parallel” means that an angle formed by two straightlines L13 that extend the respective center lines of the two lug grooves13 is within ±5°. When the two straight lines L13 are completelyparallel, the angle formed by the two straight lines L13 is 0°.

FIG. 7 is an enlarged view of a part of the middle land portion Rm ofthe tread pattern illustrated in FIG. 2. In FIG. 7, distances betweenprotrusion portions of the zigzag shape between the adjacent lug grooves13 are each denoted as Lz1, Lz2, . . . , Lzn, where n is a naturalnumber of three or greater. The distance Lz1 and the distance Lzn aredistances in the tire circumferential direction measured with referenceto the lug grooves 13 that are different from each other. In this case,a ratio Lzmin/Lzmax of the shortest distance Lzmin to the longestdistance Lzmax of the distances Lz1 to Lzn is preferably 0.50 or more.In other words, a ratio of a minimum value of distances betweenprotrusion portions of the zigzag shape to a maximum value of distancesbetween protrusion portions of the zigzag shape is preferably 1.05 ormore. The ratio Lzmin/Lzmax of 0.50 or more means that distances betweenprotrusion portions are not evenly distributed. Rather than distributingevenly, by varying distances between protrusion portions, the dispersionof the sound generated when the pneumatic tire 10 contacts the roadsurface is improved, and the pattern noise is improved. Note that theminimum value of the distances Lz1, Lz2, . . . , Lzn is 3.0 mm.

Additionally, in FIG. 7, distances in the tire circumferential directionbetween the connection portions of the plurality of sipes 16 with thecircumferential main groove 11A on the inner side in the tire widthdirection, the plurality of sipes 16 provided between the adjacent luggrooves 13, are each denoted as Ls1, Ls2, . . . , Lsn, where n is anatural number of three or greater. The distances Ls1, Ls2, . . . , Lsnare distances in the tire circumferential direction measured withreference to the connection portion of the inner side linear portion ST1with the circumferential main groove 11A. The distance Ls1 and thedistance Lsn are distances in the tire circumferential direction allmeasured with reference to the lug grooves 13 that are different fromeach other. In this case, a relationship between the distance Ls1 andthe distance Lsn is preferably Ls1<Lsn. In other words, the distance Lsnof one end in the tire circumferential direction is preferably greaterthan the distance Ls1 of the other end. By varying distances between theinner side linear portion ST1 of the sipe 16 having the Z-shape, theedge effect is exhibited in a wider angle, and the snow performance canbe improved. Note that the minimum value of the distances Ls1, Ls2, . .. , Lsn is 2.5 mm.

In FIG. 7, distances in the tire circumferential direction betweenprotrusion portions of the connection portions of the plurality of sipes16 with the circumferential main groove 12A on the outer side in thetire width direction, the plurality of sipes 16 provided between theadjacent lug grooves 13, are each denoted as Lz1, Lz2, . . . , Lzn,where n is a natural number of three or greater. The distance Lz1 andthe distance Ls1 are distances in the tire circumferential directionmeasured with reference to the identical lug groove 13. Because theidentical lug groove 13 is used as a reference, the distance Lz1 and thedistance Ls1 have an inner side-outer side relationship in the tirewidth direction and are in corresponding positions. Also, the distanceLzn and the distance Lsn are distances in the tire circumferentialdirection measured with reference to the identical lug groove 13.Because the identical lug groove 13 is used as a reference, the distanceLzn and the distance Lsn have an inner side-outer side relationship inthe tire width direction and are in corresponding positions. In thiscase, preferably, Ls1<Lz1 and Lsn>Lzn. In other words, in the tirecircumferential direction, the relationship between the distance Ls1 andthe distance Lz1 that are in corresponding positions is preferably suchthat the distance Lz1 at a position on the outer side in the tire widthdirection is greater than the distance Ls1 at a position on the innerside in the tire width direction. Because the distance Lz1 is greaterthan the distance Ls1, the length of the sipe in the extension directionincreases, which increases the edge effect and improves snowperformance. Additionally, in the tire circumferential direction, therelationship between the distance Lsn and the distance Lzn that are incorresponding positions is preferably such that the distance Lzn at aposition on the outer side in the tire width direction is less than thedistance Lsn at a position on the inner side in the tire widthdirection. Because the distance Lzn is less than the distance Lsn, thelength of the sipe in the extension direction increases, which increasesthe edge effect and improves snow performance.

In FIG. 7, the sipe 16 is connected to the edge having the zigzag shapeat a maximum amplitude position of the width W3 that is two-times anamplitude of the edge having a zigzag shape in the tire width direction.Accordingly, when stress is applied in the tire circumferentialdirection, stress applied to the protrusion portion that is prone tochip can be distributed along the groove wall of the sipe 16, and thetire chip resistance performance is improved. For example, when stressis applied in the tire circumferential direction as indicated by arrowYA, stress can be distributed along the groove wall of the sipe 16 asindicated by arrow YB. In this way, the tire chip resistance performanceof the protrusion portion that is prone to chip is improved.

FIG. 8A is an enlarged view of a part of the middle land portion Rm ofthe tread pattern illustrated in FIG. 2. FIG. 8B is an enlarged viewillustrating a part of FIG. 8A. In FIGS. 8A and 8B, the two bentportions C1, C2 of the sipe 16 are disposed on the inner side in thetire width direction of a center line RL passing through the center ofthe land portion Rm in the tire width direction. Of the two bentportions C1, C2, the bent portion C2 is positioned closer to the centerline RL than the bent portion C1. The boundary between the bent portionC2 and the linear portion ST3 is an end point K2. A distance between theend point K2 and the center line RL in the tire width direction isdenoted as db. A ratio db/W1 of the distance db to the maximum width W1of the land portion Rm in the tire width direction is preferably 0 ormore and 0.40 or less.

Here, a length in the tire circumferential direction, the length from aconnection point 23 of the sipe 16 with the circumferential main groove11A on the inner side in the tire width direction to the end point K2 onan inner side of the outer side linear portion ST3 in the tire widthdirection, is denoted as L3. A ratio L3/L1 of the length L3 to thelength L1 is preferably 0.15 or more and 0.45 or less. When the ratioL3/L1 is greater than 0.45, the number of sipes cannot be increased, andthus the snow performance does not improve, which is not preferable.When the ratio L3/L1 is less than 0.15, a length of portions connectingthe linear portion ST1 and the linear portion ST3 extending from bothedge sides of the land portion Rm (that is, the bent portion C1, thelinear portion ST2, and the bent portion C2) is reduced, and the edgeeffect is reduced and the snow performance does not improve, which isnot preferable.

Also, a ratio L3/W1 of the length L3 to the maximum width W1 ispreferably 0.15 or more and 0.65 or less. When the ratio L3/W1 is lessthan 0.15, the edge effect is reduced, and the snow performance isdegraded, which is not preferable. When the ratio L3/W1 is greater than0.65, the number of sipes cannot be increased, and thus the snowperformance does not improve, which is not preferable.

FIG. 9A is a diagram illustrating another example of the middle landportion Rm. FIG. 9B is an enlarged view illustrating a part of FIG. 9A.In FIGS. 9A and 9B, the bent portions C1, C2 of sipes 16A, 16B aredisposed on the inner side in the tire width direction of the centerline RL passing through the center of the land portion Rm in the tirewidth direction. In the sipe 16A, of the two bent portions C1, C2, thebent portion C2 is positioned closer to the center line RL than the bentportion C1. The boundary between the bent portion C2 and the linearportion ST3 is the end point K2. A distance between the end point K2 andthe center line RL in the tire width direction is denoted as Dba. Aratio Dba/W1 of the distance Dba to the maximum width W1 of the landportion Rm in the tire width direction is preferably 0 or more and 0.40or less.

Additionally, in the sipe 16B, of the two bent portions C1, C2, the bentportion C1 is positioned closer to the center line RL than the bentportion C2. The boundary between the bent portion C1 and the linearportion ST1 is the end point K1. A distance between the end point K1 andthe center line RL in the tire width direction is denoted as Dbb. Aratio Dbb/W1 of the distance Dbb to the maximum width W1 of the landportion Rm in the tire width direction is preferably 0 or more and 0.40or less.

FIG. 10A is a diagram illustrating another example of the middle landportion Rm. FIG. 10B is an enlarged view illustrating a part of FIG.10A. In FIGS. 10A and 10B, the bent portion C1 of a sipe 16C aredisposed on the inner side in the tire width direction of the centerline RL passing through the center of the land portion Rm in the tirewidth direction. The bent portion C2 of the sipe 16C is positioned onthe center line RL. More specifically, the end point K2, which is theboundary between the bent portion C2 and the linear portion ST3, ispositioned on the center line RL. In this case, the distance between theend point K2 and the center line RL in the tire width direction is 0,and thus the ratio db/W1=0. The same applies to the bent portion C2 of asipe 16D.

Thus, in the case of FIGS. 10A and 10B, the condition that a ratio of adistance in the tire width direction between the bent portion C2 that iscloser to the center line RL, the center line RL passing through amidpoint position of the land portion Rm in the tire width direction,and the center line RL to a width of the land portion Rm in the tirewidth direction is 0 or more and 0.40 or less is also satisfied. Notethat one of the two bent portions C1, C2 may be provided on the innerside in the tire width direction of the center line RL, the center lineRL passing through the midpoint position of the land portion Rm in thetire width direction, and the other may be positioned on the center lineRL.

In this manner, of the two bent portions C1, C2, provided that the ratioof a distance in the tire width direction between a bend point of thebent portion that is the closer of the two bent portions to the centerline RL, the center line RL passing through a midpoint position of theland portion Rm in the tire width direction, and the center line RL to amaximum width W1 of the land portion Rm in the tire width direction is 0or more and 0.40 or less, the following effects can be achieved. Inother words, the edge effect is increased by providing a zigzag grooveand the sipe 16 having a generally Z-shape. When the bend point havingthe generally Z-shape and the zigzag portion are in close proximity, theblock rigidity at or near the zig-zag portion decreases, and chippingmay occur. Thus, by providing the bend point of the sipe 16 and thezigzag portion at separated positions, the snow performance and the tirechip resistance performance can be provided in a compatible manner.

Additionally, the groove width is the maximum distance between left andright groove walls at the groove opening portion and is measured whenthe tire is mounted on a specified rim, inflated to the specifiedinternal pressure, and in an unloaded state. In configurations in whichthe land portions include notch portions or chamfered portions on theedge portions thereof, the groove width is measured with reference tothe intersection points where the tread contact surface and extensionlines of the groove walls meet, in a cross-sectional view normal to thegroove length direction. Additionally, in a configuration in which thegrooves extend in a zigzag-like or wave-like manner in the tirecircumferential direction, the groove width is measured with referenceto the center line of the amplitude of the groove walls.

The tire ground contact edge T is defined as a maximum width position inthe tire axial direction of the contact surface between the tire and aflat plate when the tire is mounted on a specified rim, inflated to aspecified internal pressure, placed perpendicular to the flat plate in astatic state, and loaded with a load corresponding to a specified load.

Here, “specified rim” refers to an “applicable rim” defined by the JapanAutomobile Tyre Manufacturers Association Inc. (JATMA), a “Design Rim”defined by the Tire and Rim Association, Inc. (TRA), or a “MeasuringRim” defined by the European Tyre and Rim Technical Organisation(ETRTO). Additionally, “specified internal pressure” refers to a“maximum air pressure” defined by JATMA, to the maximum value in “TIRELOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined by TRA, or to“INFLATION PRESSURES” defined by ETRTO. Additionally, “specified load”refers to a “maximum load capacity” defined by JATMA, the maximum valuein “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” defined byTRA, or “LOAD CAPACITY” defined by ETRTO. However, in the case of JATMA,for a tire for a passenger vehicle, the specified internal pressure isan air pressure of 180 kPa, and the specified load is 88% of the maximumload capacity.

Relationship Between Sipe and Raised Bottom Portion of Lug Groove

Here, the two-dimensional portion of the sipe 16 in the land portion Rmis provided at an end portion on an inner side of the sipe 16 in thetire width direction. On the other hand, the three-dimensional portionof the sipe 16 in the land portion Rm is provided at an end portion onan outer side of the sipe 16 in the tire width direction. Also, asdescribed above, in the land portion Rm, the raised bottom portion 130of the lug groove 13 is provided at an open end on the inner side of thelug groove 13 in the tire width direction. Thus, the raised bottomportion 130 is provided at an open end on an identical side to an endportion of the sipe 16 at which the two-dimensional portion is provided,among open ends on both sides of the lug groove 13. In the lug groove13, the raised bottom portion 130 is provided at an end portion on anidentical side to an end portion of the sipe at which thetwo-dimensional portion having lower rigidity than the three-dimensionalportion is provided. By providing the raised bottom portion 130 on theend portion on the two-dimensional portion side with low rigidity toincrease the rigidity, the rigidity can be made uniform for the tirecircumferential direction.

Moreover, the raised bottom portion is not provided at an open end on anidentical side to an end portion of the sipe 16 at which thethree-dimensional portion is provided, among open ends on both sides ofthe lug groove 13. The raised bottom portion 130 is provided only at theend portion on the inner side in the tire width direction where thetwo-dimensional portion is provided, and the raised bottom portion isnot provided at the end portion on the outer side in the tire widthdirection where the three-dimensional portion is provided, and thus, areduction in drainage performance can be suppressed.

Note that, due to the manufacturing convenience of the pneumatic tire10, a sipe wall surface having a straight shape may be provided on anouter side of the three-dimensional portion in the tire width directionin any cross-sectional view (cross-sectional views including the sipewidth direction and the sipe depth direction), where the sipe lengthdirection is the normal direction. The portion having a straight shapeprovided for such manufacturing convenience is included in thethree-dimensional portion. In other words, a sipe wall surface having astraight shape provided in a range of 15% of the sipe length from an endportion on the outer side of the sipe 16 in the tire width direction isconsidered to be a portion of the three-dimensional portion.

FIG. 11 is a cross-sectional view of the lug groove 13 along anextension direction. A ratio DL/Dg of a groove depth DL of the luggroove 13 to a groove depth Dg of the circumferential main groove 11A ispreferably 0.50 or more and 0.85 or less. When the ratio DL/Dg isgreater than 0.85, block rigidity decreases and wear resistanceperformance decreases, which is not preferable. When the ratio DL/Dg isless than 0.50, the snow performance is degraded, which is notpreferable.

As illustrated in FIG. 11, the raised bottom portion 130 is provided ata connection portion of the lug groove 13 with the circumferential maingroove 11A. A ratio of a groove depth of a portion where the raisedbottom portion 130 is provided to a groove depth of a portion where theraised bottom portion 130 is not provided, in other words, a ratio Du/DLof a groove depth Du of the lug groove 13 in the raised bottom portion130 to the groove depth DL of the lug groove 13 is preferably 0.40 ormore and 0.80 or less. When the ratio Du/DL is less than 0.40, drainageperformance is degraded, which is not preferable. When the ratio Du/DLis greater than 0.80, sufficient block rigidity will not be obtained,and wear resistance performance decreases, which is not preferable.

In FIG. 11, a depth that is 80% of the groove depth DL of the lug groove13 (the dot-dash line in FIG. 11) is denoted as the depth 0.8DL. Thelength of the raised bottom portion 130 in the tire width direction atthe depth 0.8DL is denoted as Wu. A ratio Wu/W1 of the length Wu of theraised bottom portion 130 in the tire width direction to the maximumwidth W1 (see FIG. 4) of the land portion Rm in the tire width directionis preferably 0.15 or more and 0.50 or less. When the ratio Wu/W1 isless than 0.15, sufficient block rigidity will not be obtained, anduneven wear resistance performance will be negatively affected, which isnot preferable. When the ratio Wu/W1 is greater than 0.50, the blockrigidity of the sipe 16 on the three-dimensional portion side will betoo high, and uneven wear resistance performance will be negativelyaffected, which is not preferable.

Shoulder Land Portion

FIG. 12 is an enlarged view of a part of the shoulder land portion Rs ofthe tread pattern illustrated in FIG. 2. In FIG. 12, the land portion Rson the outer side of the circumferential main groove 12B in the tirewidth direction includes the sipe (hereinafter, also referred to as ashoulder sipe) 17. A length (in other words, a width) of thethree-dimensional portion of the sipe 17 in the tire width direction isdenoted as Ws2. The length Ws2 is a length (in other words, a width) inthe tire width direction from the edge of the circumferential maingroove 12B in the land portion Rs to an end on the outer side of thethree-dimensional portion of the sipe 17 in the tire width direction.Additionally, a length from the edge of the circumferential main groove12B in the land portion Rs to the ground contact edge T, in other words,the ground contact width of the land portion Rs in the tire widthdirection is denoted as Ws1. In this case, a ratio Ws2/Ws1 is preferably0.25 or more and 0.65 or less. When the ratio Ws2/Ws1 is less than 0.25,sufficient block rigidity will not be obtained, and uneven wearresistance performance will be negatively affected. When the ratioWs2/Ws1 is greater than 0.65, block rigidity on the three-dimensionalportion side will be too high, and pattern noise will be negativelyaffected, which is not preferable.

In FIG. 12, the land portion Rs includes the plurality of shoulder luggrooves 14A, 14B extending from the circumferential main groove 12B onthe inner side in the tire width direction toward the outer side in thetire width direction. The plurality of shoulder lug grooves 14A, 14Bpreferably extend at least to the ground contact edge T. By extendingthe plurality of shoulder lug grooves 14A, 14B to the ground contactedge T, drainage performance can be improved.

The raised bottom portion 140A is provided at an open end of theshoulder lug groove 14A to the circumferential main groove 12B. Also,the raised bottom portion 140B is provided at an open end of theshoulder lug groove 14B to the circumferential main groove 12B. Althoughthe rigidity is increased by the region 20C of three-dimensional portionprovided between the shoulder lug groove 14A and the shoulder lug groove14B, by providing the raised bottom portion 140A and the raised bottomportion 140B at the open ends to the circumferential main groove 12B,which tends to be less rigid, the rigidity can be made uniform in thetire circumferential direction.

Incidentally, in the land portion Rs, a length of the edge having azigzag shape between adjacent shoulder lug grooves 14A, 14B in the tirecircumferential direction is denoted as Ls1. Additionally, a distancebetween protrusion portions of the zigzag shape in the tirecircumferential direction is denoted as Ls2. In this case, a ratioLs2/Ls1 is preferably 0.15 or more and 0.55 or less. When the ratioLs2/Ls1 is less than 0.15, recesses/protrusions of the zigzag shape areexcessively fine and chip easily, which is not preferable. When theratio Ls2/Ls1 is greater than 0.55, the edge effect cannot besufficiently achieved, and the snow performance does not improve.

Further, in the land portion Rs, a ground contact width in the tirewidth direction is denoted as Ws1. Additionally, in the land portion Rs,a length that is two-times an amplitude of the zigzag shape of the edgeon the circumferential main groove 12B side in the tire width directionis denoted as Ws3. The length Ws3 is a length (in other words, a width)of a protrusion portion of the zigzag shape in the tire width direction.In this case, a ratio Ws3/Ws1 is preferably 0.02 or more and 0.15 orless. When the ratio Ws3/Ws1 is less than 0.02, the edge effect does notoccur, and the snow performance does not improve. When the ratio Ws3/Ws1is greater than 0.15, drainage properties are impaired, and drainageperformance is degraded.

Note that while the land portion Rs on the outer side of thecircumferential main groove 12B in the tire width direction has beendescribed above, similar description applies to the land portion Rs onthe outer side of the circumferential main groove 12A in the tire widthdirection.

Inclination Direction of Each Sipe

FIG. 13 is a diagram illustrating the inclination direction of each sipein FIG. 2. FIG. 13 is an enlarged view illustrating a part of FIG. 2. InFIG. 13, the inclination direction of the center sipes 15 provided inthe center land portion Rc with respect to the tire circumferentialdirection is denoted by an arrow YC. On the other hand, the inclinationdirection of the middle sipes 16, 16 provided in the middle land portionRm with respect to the tire circumferential direction is denoted by anarrow YM1 and an arrow YM2. Thus, the inclination directions of themiddle sipes 16, 16 provided in the middle land portion Rm are identicalto each other. The inclination directions of the middle sipes 16, 16 andthe inclination direction of the center sipe 15 provided in the centerland portion Rc are different from each other. The inclinationdirections of the sipes differs between the middle land portion Rm andthe center land portion Rc, and thus edge effects in other directionsoccur, and the handling on snow performance is improved.

Three-Dimensional Portion of Composite Sipe

FIG. 14 is a cross-sectional view illustrating an example of athree-dimensional portion of the composite sipe 16 in FIG. 2. FIG. 14 isa view illustrating a cross section in which a section of thethree-dimensional portion of the composite sipe 16 is cut in a planeorthogonal to the extension direction (in other words, the lengthdirection) of the sipe. In FIG. 14, a length in the sipe depthdirection, from an open end 9A to the road contact surface of thecomposite sipe 16 to a groove bottom 9B, in other words, a groove depth,is DS. A groove width (in other words, a sipe width) of the compositesipe 16 is Ts.

The composite sipe 16 in the vicinity of the open end 9A is a linearportion 9 along the sipe depth direction. The composite sipe 16 has ashape that curves or bends with respect to the sipe depth direction. Anamplitude of the curve or bend in the sipe width direction centered on aline 9L, the line 9L an extension of the center line of the linearportion 9, is As. The ratio As/Ts of the amplitude As to the groovewidth Ts is preferably 0.40 or more and 0.80 or less. When the ratioAs/Ts is greater than 0.80, releasing of the mold during vulcanizationmolding becomes poor, and a fault occurs, which is not preferable. Whenthe ratio As/Ts is less than 0.40, inclination cannot be suppressed andthe block rigidity does not increase, and wear resistance performance isnot improved, which is not preferable.

Additionally, in FIG. 14, one period length of curve or bend of thecomposite sipe 16 is S. The composite sipe 16 preferably has a curvedshape or a bent shape that is one period length or more and three periodlengths or less. When the period length is less than one period length,the effect of suppressing inclination will be insufficient and blockrigidity will not increase, which is not preferable. When the periodlength is greater than three period lengths, releasing of the moldduring vulcanization molding is poor, and a fault occurs, which is notpreferable.

Note that the other composite sipes 15 and 17 in FIG. 2 have identicalstructures to the composite sipe 16 described above.

Groove Depth

FIG. 15 is a cross-sectional view of the sipe 16 of FIG. 5 along theextension direction. FIG. 15 illustrates the two-dimensional portion andthe three-dimensional portion without distinction. A ratio DS/Dg of agroove depth DS of the sipe 16 to a groove depth Dg of thecircumferential main groove 11A is preferably 0.50 or more and 0.85 orless. When the ratio DS/Dg is greater than 0.85, block rigiditydecreases and wear resistance performance decreases, which is notpreferable. When the ratio DS/Dg is less than 0.50, the edge effect isnot sufficient, and snow performance is degraded, which is notpreferable.

As illustrated in FIG. 15, a raised bottom portion 160 is provided at aconnection portion of the sipe 16 with the circumferential main groove11A. The raised bottom portion 160 is a sipe raised bottom portionprovided in the sipe 16. A ratio DS1/DS of a groove depth DS1 of thesipe 16 at the raised bottom portion 160 to the groove depth DS of thesipe 16 is preferably 0.50 or more and 0.85 or less. When the ratioDS1/DS is greater than 0.85, block rigidity decreases and wearresistance performance decreases, which is not preferable. When theratio DS1/DS is less than 0.50, the edge effect is not sufficient, andsnow performance is degraded, which is not preferable.

Also, for the sipe 15 of the center land portion Rc and the sipe 17 ofthe shoulder land portions Rs, a ratio of a groove depth of each of thesipes 15, 17 to the groove depth Dg of the circumferential main groove11A is preferably 0.50 or more and 0.85 or less. When the ratio isgreater than 0.85, block rigidity decreases and wear resistanceperformance decreases, which is not preferable. When the ratio is lessthan 0.50, the edge effect is not sufficient, and snow performance isdegraded, which is not preferable.

EXAMPLES

Table 1 to Table 4 are tables showing the results of performance testsof pneumatic tires according to embodiments of the present technology.In the performance tests, mutually differing pneumatic tires wereevaluated for uneven wear resistance performance, braking on snowperformance, handling on snow performance, and drainage performance. Inthese performance tests, a test tire having a size of 225/65R17 102H wasmounted on a rim having a rim size of 17×7.0J, and inflated to an airpressure of 230 kPa. Additionally, a front engine-front drive (FF) sportutility vehicle (SUV) with an engine displacement of 2500 cc was used asa test vehicle.

In the evaluation of uneven wear resistance performance, the testvehicle traveled for ten thousand km on the paved road, and then theamount of wear of the center land portion and the amount of wear of theshoulder land portion were measured, and the uneven wear amount ratiowas calculated. Uneven wear amount ratios are expressed as index valuesand evaluated with Conventional Example being assigned as the reference(100) described below. Larger index values are preferable.

The braking on snow performance was evaluated as index values derivedfrom the braking distance at a speed of 30 km/h on snow-covered roadsurfaces. Results of the evaluation are expressed as index values andevaluated with Conventional Example being assigned as the reference(100) described below. Larger values are preferable.

The handling on snow performance was evaluated as index values derivedfrom the feelings by the test driver of steering stability onsnow-covered road surfaces. Results of the evaluation are expressed asindex values and evaluated with Conventional Example being assigned asthe reference (100) described below. Larger values are preferable.

The pattern noise performance was evaluated by measuring vehicleinterior noise in a vehicle traveling at a speed of 100 km/h. The entirefrequency band of the vehicle interior noise was covered. The noisemeasured value in dB was used for the evaluation that is based onConventional Example described below as reference (0 dB). Smaller valuesare preferable.

The pneumatic tires of Examples 1 to 18 are tires provided with two ormore circumferential main grooves in a half region demarcated by thetire equatorial plane, and a plurality of land portions defined by thecircumferential main grooves. Additionally, the center land portion thatis the closest of the plurality of land portions to the tire equatorialplane is provided with a center sipe extending in the tire widthdirection, and the center sipe is a composite sipe including atwo-dimensional portion and three-dimensional portions provided on bothsides of the two-dimensional portion in the tire width direction.Furthermore, the middle land portion adjacent to an outer side of thecenter land portion in the tire width direction is provided with amiddle sipe extending in the tire width direction, and the middle sipehas a Z-shape and is a composite sipe including a two-dimensionalportion provided on the inner side in the tire width direction and athree-dimensional portion provided on an outer side of thetwo-dimensional portion in the tire width direction.

Pneumatic tires of Examples 1 to 18 were set as shown in Tables 1 to 4.In other words, pneumatic tires are prepared that are each with andwithout both ends of the center sipe being 3D sipes while the center ofthe center sipe being a 2D sipe, with and without a ratio Wc3/Wc of thelength Wc3 of a three-dimensional portion of the center sipe to thelength We of the entire center sipe being 0.30 or more and 0.70 or less,with and without both ends of the middle sipe being 3D sipes while aninner side of the middle sipe in the tire width direction being a 2Dsipe, with and without the ratio Wc2/Wm of the length Wc2 of athree-dimensional portion of the middle sipe to the length Wm of theentire middle sipe being 0.25 or more and 0.80 or less, with and withoutthe ratio db/W1 of a distance in the tire width direction between thebent portion that is the closer of the two bent portions of the Z-shapeof the middle sipe to the center line, the center line passing throughthe midpoint position of the middle land portion in the tire widthdirection, and the center line to a width of the middle land portion inthe tire width direction being 0 or more and 0.40 or less, with andwithout both ends of the shoulder sipe being 2D sipes while an innerside of the shoulder sipe in the tire width direction being a 3D sipe,and with and without the ratio Ws2/Ws1 of the length Ws2 of thethree-dimensional portion of the shoulder sipe to the length Ws1 of theentire shoulder sipe being 0.25 or more and 0.65 or less. Note thatabove pneumatic tires are each with the ratio Lzmin/Lzmax of a minimumvalue of distances between protrusion portions of the zigzag shape to amaximum value of distances between protrusion portions of the zigzagshape being 0.50 or more.

The pneumatic tire of Conventional Example is a tire in which the entiresipe provided in the land portion is a 2D sipe. The pneumatic tire ofComparative Example 1 is a tire in which the entire sipe provided in theland portion is a 3D sipe. The pneumatic tire of Comparative Example 2is a tire in which the center of the center sipe is a 3D sipe, bothsides thereof are 2D sipes, the inner side of the middle sipe in thetire width direction is a 2D sipe, the outer side thereof is a 3D sipe,the inner side of the shoulder sipe is a 3D sipe, and the outer sidethereof is a 2D sipe. The pneumatic tire of Comparative Example 3 is atire in which the center of the center sipe is a 2D sipe, both sidesthereof are 3D sipes, the inner side of the middle sipe in the tirewidth direction is a 3D sipe, the outer side thereof is a 2D sipe, theinner side of the shoulder sipe is a 3D sipe, and the outer side thereofis a 2D sipe. The pneumatic tire of Comparative Example 4 is a tire inwhich the center of the center sipe is a 2D sipe, both sides thereof are3D sipes, the inner side of the middle sipe in the tire width directionis a 2D sipe, the outer side thereof is a 3D sipe, the inner side of theshoulder sipe is a 2D sipe, and the outer side thereof is a 3D sipe.

Note that in Tables 1 to 4, “2D” of the sipe shape indicates that thesipe is a sipe formed only from a two-dimensional portion. “3D” of thesipe shape indicates that the sipe is formed only from athree-dimensional portion. “2D+3D” of the sipe shape indicates acomposite sipe formed from a two-dimensional portion and athree-dimensional portion.

The pneumatic tires were evaluated for uneven wear resistanceperformance, braking on snow performance, handling on snow performance,pattern noise performance, and drainage performance by the evaluationmethods described above. The results are shown in Tables 1 to 4.

As shown in Tables 1 to 4, good results were obtained when both ends ofthe center sipe being 3D sipes while the center of the center sipe beinga 2D sipe, when the ratio Wc3/Wc of the length Wc3 of athree-dimensional portion of the center sipe to the length We of theentire center sipe being 0.30 or more and 0.70 or less, when both endsof the middle sipe being 3D sipes while the inner side of the middlesipe in the tire width direction being a 2D sipe, when a ratio Wc2/Wm ofthe length Wc2 of a three-dimensional portion of the middle sipe to thelength Wm of the entire middle sipe being 0.25 or more and 0.80 or less,when the ratio db/W1 of a distance in the tire width direction betweenthe bent portion that is the closer of the two bent portions of theZ-shape of the middle sipe to the center line, the center line passingthrough the midpoint position of the middle land portion in the tirewidth direction, and the center line to a width of the middle landportion in the tire width direction being 0 or more and 0.40 or less,when the ratio Lzmin/Lzmax of a minimum value of distances betweenprotrusion portions of the zigzag shape to a maximum value of distancesbetween protrusion portions of the zigzag shape being 0.50 or more, whenboth ends of the shoulder sipe being 2D sipes while the inner side ofthe shoulder sipe in the tire width direction being a 3D sipe, and whenthe ratio Ws2/Ws1 of the length Ws2 of the three-dimensional portion ofthe shoulder sipe to the length Ws1 of the entire shoulder sipe being0.25 or more and 0.65 or less.

TABLE 1-1 Conventional Comparative Comparative example Example 1 Example2 Sipe form All 2D All 3D 2D + 3D Structure of center sipe 2D 3D 3D incenter, 2D in both ends Ratio Wc3/Wc — 1.00 0.48 Structure of middlesipe — 3D 2D on inner side, 3D on outer side Ratio Wc2/Wm — 1.00 0.53Shape of middle sipe Straight Straight Z-shape Ratio Db/W1 — — 0.20Shape of edge on outer side Straight Straight Zigzag of middle landportion in tire width direction Structure of shoulder sipe Straight 3D3D on inner side, 2D on outer side Ratio Ws2/Ws1 — 1.00 0.43 Uneven wearresistance 100 112 105 performance (index value) Braking on snow 100 107106 performance (index value) Handling on snow 100 108 108 performance(index value) Pattern noise performance 0.0 +0.8 0.0 [dB]

TABLE 1-2 Comparative Comparative Example 3 Example 4 Example 1 Example2 Sipe form 2D + 3D 2D + 3D 2D + 3D 2D + 3D Structure of 2D in center,2D in center, 2D in center, 2D in center, center sipe 3D in both ends 3Din both ends 3D in both ends 3D in both ends Ratio Wc3/Wc 0.48 0.48 0.480.28 Structure of 3D on inner side, 2D on inner side, 2D on inner side,2D on inner side, middle sipe 2D on outer side 3D on outer side 3D onouter side 3D on outer side Ratio Wc2/Wm 0.53 0.53 0.53 0.53 Shape ofmiddle Z-shape Z-shape Z-shape Z-shape sipe Ratio Db/W1 0.20 0.20 0.200.20 Shape of edge on Zigzag Zigzag Zigzag Zigzag outer side of middleland portion in tire width direction Structure of 3D on inner side, 2Don inner side, 3D on inner side, 3D on inner side, shoulder sipe 2D onouter side 3D on outer side 2D on outer side 2D on outer side RatioWs2/Ws1 0.43 0.43 0.43 0.43 Uneven wear 104 102 110 103 resistanceperformance (index value) Braking on snow 106 106 106 106 performance(index value) Handling on snow 108 108 108 104 performance (index value)Pattern noise 0.0 0.0 0.0 0.0 performance [dB]

TABLE 2 Example Example Example Example Example Example 3 4 5 6 7 8 Sipeform 2D + 3D 2D + 3D 2D + 3D 2D + 3D 2D + 3D 2D + 3D Structure of 2D in2D in 2D in 2D in 2D in 2D in center sipe center, center, center,center, center, center, 3D in 3D in 3D in 3D in 3D in 3D in both endsboth ends both ends both ends both ends both ends Ratio Wc3/Wc 0.30 0.700.82 0.48 0.48 0.48 Structure of 2D on 2D on 2D on 2D on 2D on 2D onmiddle sipe inner inner inner inner inner inner side, 3D side, 3D side,3D side, 3D side, 3D side, 3D on outer on outer on outer on outer onouter on outer side side side side side side Ratio Wc2/Wm 0.25 0.80 0.530.23 0.25 0.80 Shape of middle Z-shape Z-shape Z-shape Z-shape Z-shapeZ-shape sipe Ratio Db/W1 0.20 0.20 0.20 0.20 0.20 0.20 Shape of edgeZigzag Zigzag Zigzag Zigzag Zigzag Zigzag on outer side of middle landportion in tire width direction Structure of 3D on 3D on 3D on 3D on 3Don 3D on shoulder sipe inner inner inner inner inner inner side, 2Dside, 2D side, 2D side, 2D side, 2D side, 2D on outer on outer on outeron outer on outer on outer side side side side side side Ratio Ws2/Ws10.43 0.43 0.43 0.43 0.43 0.43 Uneven wear 104 108 110 102 106 108resistance performance (index value) Braking on 106 106 106 106 106 106snow performance (index value) Handling on 102 110 108 102 104 108 snowperformance (index value) Pattern noise 0.0 0.0 +0.4 0.0 0.0 0.0performance [dB]

TABLE 3 Example Example Example Example Example 9 10 11 12 13 Sipe form2D + 3D 2D + 3D 2D + 3D 2D + 3D 2D + 3D Structure of center 2D in 2D in2D in 2D in 2D in sipe center, 3D center, 3D center, 3D center, 3Dcenter, 3D in both in both in both in both in both ends ends ends endsends Ratio Wc3/Wc 0.48 0.48 0.48 0.48 0.48 Structure of middle 2D on 2Don 2D on 2D on 2D on sipe inner side, inner side, inner side, innerside, inner side, 3D on 3D on 3D on 3D on 3D on outer side outer sideouter side outer side outer side Ratio Wc2/Wm 0.82 0.53 0.53 0.53 0.53Shape of middle sipe Z-shape Z-shape Z-shape Z-shape Z-shape Ratio Db/W10.20 0.00 0.20 0.30 0.40 Shape of edge on Zigzag Zigzag Zigzag ZigzagZigzag outer side of middle land portion in tire width directionStructure of shoulder 3D on 3D on 3D on 3D on 3D on sipe inner side,inner side, inner side, inner side, inner side, 2D on 2D on 2D on 2D on2D on outer side outer side outer side outer side outer side RatioWs2/Ws1 0.43 0.43 0.43 0.43 0.43 Uneven wear 108 108 110 110 108resistance performance (index value) Braking on snow 106 106 106 106 104performance (index value) Handling on snow 108 108 108 108 106performance (index value) Pattern noise +0.5 0.0 0.0 0.0 0.0 performance[dR]

TABLE 4 Example Example Example Example Example 14 15 16 17 18 Sipe form2D + 3D 2D + 3D 2D + 3D 2D + 3D 2D + 3D Structure of center sipe 2D in2D in 2D in 2D in 2D in center, center, center, center, center, 3D in 3Din 3D in 3D in 3D in both ends both ends both ends both ends both endsRatio Wc3/Wc 0.48 0.48 0.48 0.48 0.48 Structure of middle sipe 2D on 2Don 2D on 2D on 2D on inner inner inner inner inner side, 3D side, 3Dside, 3D side, 3D side, 3D on outer on outer on outer on outer on outerside side side side side Ratio Wc2/Wm 0.53 0.53 0.53 0.53 0.53 Shape ofmiddle sipe Z-shape Z-shape Z-shape Z-shape Z-shape Ratio Db/Wl 0.500.20 0.20 0.20 0.20 Shape of edge on outer Zigzag Zigzag Zigzag ZigzagZigzag side of middle land portion in tire width direction Structure ofshoulder sipe 3D on 3D on 3D on 3D on 3D on inner inner inner innerinner side, 2D side, 2D side, 2D side, 2D side, 2D on outer on outer onouter on outer on outer side side side side side Ratio Ws2/Ws1 0.43 0.230.25 0.65 0.67 Uneven wear resistance 104 104 106 108 108 performance(index value) Braking on snow 102 106 106 106 106 performance (indexvalue) Handling on snow 102 102 104 110 110 performance (index value)Pattern noise performance 0.0 0.0 0.0 0.0 +0.6 [dB]

1-14. (canceled) 15: A pneumatic tire, comprising: a tread pattern comprising two or more circumferential main grooves provided in a half region demarcated by a tire equatorial plane, and a plurality of land portions defined by the circumferential main grooves, a center land portion that is a closest land portion of the plurality of land portions to the tire equatorial plane comprising a center sipe extending in a tire width direction; the center sipe being a composite sipe comprising a two-dimensional portion and three-dimensional portions provided on both sides of the two-dimensional portion in the tire width direction; a middle land portion that is a land portion adjacent to an outer side of the center land portion in the tire width direction comprising a middle sipe extending in the tire width direction; and the middle sipe being a composite sipe comprising a two-dimensional portion provided on an inner side in the tire width direction and a three-dimensional portion provided on an outer side of the two-dimensional portion in the tire width direction. 16: The pneumatic tire according to claim 15, wherein a ratio of a total length of the three-dimensional portions of the center sipe in the tire width direction to a length of the center sipe in the tire width direction is 0.30 or more and 0.70 or less. 17: The pneumatic tire according to claim 15, wherein the center sipe has a Z-shape with two bent portions. 18: The pneumatic tire according to claim 15, wherein a ratio of a length of the three-dimensional portion of the middle sipe in the tire width direction to a length of the middle land portion in the tire width direction is 0.25 or more and 0.80 or less. 19: The pneumatic tire according to claim 15, wherein the middle sipe has a Z-shape with two bent portions, and a ratio of a distance in the tire width direction between a bent portion that is a closer of the two bent portions to a center line, the center line passing through a midpoint position of the land portion in the tire width direction, and the center line to a width of the land portion in the tire width direction is 0 or more and 0.40 or less. 20: The pneumatic tire according to claim 15, wherein an edge on an outer side of the middle land portion in the tire width direction is a zigzag edge having a zigzag shape with recesses/protrusions that has a position periodically changing in the tire width direction and an edge on an inner side of the middle land portion in the tire width direction has a straight shape, and the three-dimensional portion of the middle sipe is connected to the zigzag edge. 21: The pneumatic tire according to claim 20, wherein the middle sipe is connected to a maximum amplitude position of the zigzag edge in the tire width direction. 22: The pneumatic tire according to claim 20, wherein a ratio of a minimum value of distances between protrusion portions of the zigzag shape to a maximum value of the distances between the protrusion portions of the zigzag shape is 0.50 or more. 23: The pneumatic tire according to claim 20, wherein the middle land portion comprises a plurality of lug grooves and, between the lug grooves that are adjacent, two or more of the middle sipes and three or more protrusion portions of the zigzag shape. 24: The pneumatic tire according to claim 23, wherein distances in a tire circumferential direction between connection portions of the two or more middle sipes with the circumferential main groove on the inner side in the tire width direction, the two or more middle sipes provided between the lug grooves that are adjacent, are Ls1, Ls2, . . . , Lsn, where n is a natural number of three or greater, and Ls1<Lsn. 25: The pneumatic tire according to claim 23, wherein distances in a tire circumferential direction between connection portions of the two or more middle sipes with a circumferential main groove on the inner side in the tire width direction, the two or more middle sipes provided between the lug grooves that are adjacent, are Ls1, Ls2, . . . , Lsn, where n is a natural number of three or greater, distances in the tire circumferential direction between the protrusion portions of connection portions of a plurality of the middle sipes with the circumferential main groove on an outer side in the tire width direction, the plurality of middle sipes provided between the lug grooves that are adjacent, are Lz1, Lz2, . . . , Lzn, where n is a natural number of three or greater, and Ls1<Lz1 and Lsn>Lzn. 26: The pneumatic tire according to claim 15, further comprising a shoulder land portion that is a land portion on an outer side of the middle land portion in the tire width direction, wherein the shoulder land portion comprises a shoulder sipe extending in the tire width direction, the shoulder sipe is a composite sipe comprising a three-dimensional portion provided on the inner side in the tire width direction and a two-dimensional portion provided on an outer side of the three-dimensional portion in the tire width direction. 27: The pneumatic tire according to claim 26, wherein a ratio of a length of the three-dimensional portion of the shoulder sipe in the tire width direction to a ground contact width of the shoulder land portion in the tire width direction is 0.25 or more and 0.65 or less. 28: The pneumatic tire according to claim 26, wherein groove wall surfaces of both sides of the circumferential main groove between the middle land portion and the shoulder land portion are wall surfaces in which zigzag edges face each other. 